Varicella zoster virus (VZV) causes chickenpox and zoster (shingles). Chickenpox is a highly contagious disease that occurs in persons with no VZV immunity. More than 90% of the. population is exposed during the first two decades of life. The disease is a severe threat to the immunosuppressed and to adults. In many cases, VZV becomes latent in dorsal root ganglion cells. Shingles, a painful chronic condition, occurs when VZV is reactivated from the latent state.
Prevention of chickenpox by vaccination is a desirable goal, and the institution of universal childhood vaccination with a live attenuated varicella vaccine is envisioned. The prior art has reported the propagation of VZV in various cell culture systems and the use of live, attenuated, cell-free VZV as a vaccine. U.S. Pat. No. 3,985,615 describes the production in guinea pig primary embryonic cells of the attenuated Oka strain of VZV, suitable for vaccine use. U.S. Pat. No. 4,008,317 describes the cultivation of a temperature-sensitive mutant of VZV in WI-38 cells for use as a vaccine stablilizer. Compositions useful for the maintainance of viable VZV, such as SPGA, are also known in the art.
The major limitation to commercial production of a VZV vaccine is the yield of cell-free VZV from cell culture systems known in the art. Cell-free VZV yields are improved by about a factor of 5-20 fold by application of the new process of this invention.
Thus, the present invention is a process for the production of a live, attenuated, cell-free VZV vaccine in high yield.